Archive for April, 2014

One current ‘when-I-get-spare-time-in-the-evening’ project is to explore how different keys sounded before the advent of equal temperament. Partly out of interest and partly because whenever I hear/read discussions of how keys got their distinctive characteristics (for example in answers to this question on the Musical Practise and Performance Stack Exchange) temperament is raised as an issue or explanation.

The story, as I was told it, has Pythagoras walking down a street in ancient Greece when he hears the sound coming from blacksmiths hammering iron bars. He notes that some hammerings produce harmonious sounds and some do not. On further investigation into the pleasing sounds Pythagoras discovered the frequency ratios behind the octave (a doubling of the frequency) and the perfect fifth (adding a half to the bar length, a frequency ratio of 3:2). Thus the Pythagorean Temperament is formed solely of repeated perfect fifths and octaves.

So how might that look in Clojure? This is me working through my understanding so I’m going to keep it simple. But first up I need some helper functions

I can now just write out the names of the fifths and fourths we are interested in. Starting from A the first few give us the notes we need for a scale of A major: A, B, C♯, D, E, F♯, and G♯, and if we take the first twelve of each we get to common notes before needing double sharps, double flats, etc. (N.B. We’ll come back to that “etc”!)

That’s a fun start, but it has left me with a question. Overtone seems to use MIDI notes as the underlying note ‘name’, but MIDI notes give enharmonically equivalent notes the same name. So, for example, the MIDI note 73 is C♯ and D♭ but in Pythagorean Temperament rooted on A they have different pitches. Benson refers to this by changing the familiar “circle of fifths” to the “spiral of fifths” noting that the “Pythagorean spiral never joins up”, i.e. after double sharps there will be triple sharps etc. without ever reaching enharmonic equivalence. I’ll check on the Overtone mailing list to see how important/correct my sense of underlying MIDI notes is.